For a long time it was believed that parity symmetry (the interchange of left and right) held in every interaction. In 1956, the Chinese-American physicist Chien-Shiung Wu showed that it is in fact violated, specifically in the interaction . T.D Lee and C.N. Yang had suggested to her that pseudo scalar quantities such as , where – is the nuclear spin and is the electron momentum – might actually not be invariant under parity conservation. No physicist had ever measured such a quantity, so C. S. Wu quickly devised a novel experiment to do so. In this problem we will follow a calculation of Wu to investigate why parity conservation implies that the expectation value of the chosen pseudo-scalar is 0

- The parity operator acts on a wave function as follows . Show for an odd or even wavefunction viz. (odd: , even: ) that the probability the wave function is between and is invariant under parity.
- Show that parity invariance implies that

**References:**

*The discovery of the parity violation in weak interactions and its recent developments*

*Chien-Shiung Wu*

*Published in: Lect.Notes Phys. 746 (2008), 43-70*

*Experimental Test of Parity Conservation in Beta Decay*

*C. S. Wu, E. Ambler, R. W. Hayward, D. D. Hoppes, and R. P. Hudson*

*Phys. Rev. 105, 1413 – Published 15 February 1957*